This invention relates generally to golf balls and, in particular, golf ball cores formed of a polymer composition including a halogenated organosulfur compound and resilient regrind.
Conventional golf balls can be divided into two general classes: solid and wound. Solid golf balls include one-piece, two-piece (i.e., solid core and a cover), and multi-layer (i.e., solid core of one or more layers and/or a cover of one or more layers) golf balls. Wound golf balls typically include a solid, hollow, or fluid-filled center, surrounded by a tensioned elastomeric material, and a cover. Solid balls have traditionally been considered longer and more durable than wound balls, but also lack a particular xe2x80x9cfeelxe2x80x9d provided by the wound construction.
By altering ball construction and composition, manufacturers can vary a wide range of playing characteristics, such as compression, velocity, and spin, each of which can be optimized for various playing abilities. One golf ball component, in particular, that many manufacturers are continually looking to improve is the center or core. The core becomes the xe2x80x9cenginexe2x80x9d of the golf ball when hit with a club head. Generally, golf ball cores and/or centers are constructed with a polybutadiene-based polymer composition. Compositions of this type are constantly being altered in an effort to provide a higher coefficient of restitution (xe2x80x9cCORxe2x80x9d) while at the same time resulting in a lower compression which, in turn, can lower the golf ball spin rate, provide better xe2x80x9cfeel,xe2x80x9d or both. This is a difficult task, however, given the physical limitations of currently-available polymers. As such, there remains a need for novel and improved golf ball core compositions.
It has been determined that, upon that addition of a halogenated organosulfur compound or the salts thereof, in particular, pentachlorothiophenol (xe2x80x9cPCTPxe2x80x9d) salt, to polybutadiene rubber compositions, that golf ball cores may be constructed that exhibit increased COR, decreased compression, or both. The present invention is, therefore, directed to golf ball centers and cores that include a halogenated organosulfur compound, or a salt thereof, for embodiments such as these.
The present invention is directed to a two-piece golf ball including a core having a diameter of between about 1.54 and about 1.58 inches and a compression of between about 22 and about 50, the core including a polybutadiene rubber having a Mooney viscosity of less than about 50 and a halogenated organosulfur compound present in an amount of at least about 2.2 parts per hundred parts of polybutadiene rubber, the halogenated organosulfur compound having the formula: 
where R1-R5 are C1-C8 alkyl groups; halogen groups; thiol groups; carboxylated groups; sulfonated groups; or hydrogen; and a regrind filler present in an amount of from about 5 parts to about 26.5 parts per hundred parts of polybutadiene rubber; and a cover having a thickness of between about 0.05 inches and about 0.1 inches, the cover including a first ionomeric material and a second ionomeric material; wherein the golf ball has a coefficient of restitution of at least about 0.813 when measured at 125 ft/s.
The regrind is vulcanized polybutadiene rubber that contains a substantially greater amount of the trans-polybutadiene isomer than prior to vulcanization and is preferably present in an amount of from about 10.6 parts to about 19.7 parts per hundred parts of polybutadiene rubber. The core of the golf ball preferably has a diameter of between about 1.54 and about 1.57 inches. The amount of the trans-polybutadiene isomer in the vulcanized polybutadiene rubber is between about 10% and about 60%.
The polybutadiene composition further comprises an xcex1,xcex2-unsaturated carboxylic acid or a metal salt thereof, an organic peroxide, and a second filler. Preferably, the xcex1,xcex2-unsaturated carboxylic acid or a metal salt thereof is present in an amount greater than about 30 parts per hundred parts of polybutadiene rubber. More preferably, the xcex1,xcex2-unsaturated carboxylic acid or a metal salt thereof is present in an amount greater than about 41 parts per hundred parts of polybutadiene rubber. The at least one of the first and second ionomeric materials may include xcex1,xcex2-unsaturated carboxylic acid groups, or the salts thereof, that have been partially- or fully-neutralized by organic fatty acids.
In a preferred embodiment, the halogenated organosulfur compound is present in an amount between about 2.2 parts and about 5 parts. Ideally, the halogenated organosulfur compound is selected from the group consisting of pentachlorothiophenol or a metal salt of pentachlorothiophenol. If the metal salt is selected, preferably the metal salt is selected from the group consisting of zinc, calcium, magnesium, sodium, and lithium and, most preferably, the metal salt is zinc.
The first and second ionomeric materials include copolymers or terpolymers of ethylene and methacrylic acid or acrylic acid partially- or fully-neutralized with salts of zinc, sodium, lithium, magnesium, potassium, calcium, manganese, or nickel. Additionally, the core includes between about 1 part and 50 parts vulcanized polybutadiene rubber per hundred parts first polybutadiene rubber and the cover has a tan* of between about 0.07 and about 0.09 measured over the range of xe2x88x9230xc2x0 C. to 20xc2x0 C.
Preferably, the first ionomeric material present in an amount between about 45% and about 55% and the second ionomeric material present in an amount between about 55% and about 45%. Additionally, the core preferably has a surface hardness and a geometric center hardness that differs from the surface hardness by between about 15 Shore D and about 20 Shore D. In a preferred embodiment, the golf ball has a coefficient of restitution of between about 0.813 and about 0.823.
The present invention is also directed to a golf ball consisting of a core having a diameter of between about 1.54 and about 1.57 inches and a compression of between about 22 and about 50, the core comprising a first polybutadiene rubber having a Mooney viscosity of less than about 50 and a halogenated organosulfur compound or the salt thereof, the halogenated organosulfur compound having the formula: 
where R1-R5 are C1-C8 alkyl groups; halogen groups; thiol groups; carboxylated groups; sulfonated groups; or hydrogen; and regrind filler present in an amount of from about 10.6 parts to about 19.7 parts per hundred parts of polybutadiene rubber; and a cover having a thickness of between about 0.05 inches and about 0.1 inches, the cover consisting essentially of a first ionomeric material and a second ionomeric material; wherein the golf ball has a coefficient of restitution of at least about 0.813 when measured at 125 ft/s.
The present invention is further directed to a golf ball including a core having a diameter of between about 1.54 and about 1.61 inches and a compression of between about 22 and about 70, the core including 1,4-polybutadiene having a cis-structure of at least about 95% and a Mooney viscosity of less than about 50; and a filler comprising a trans-regrind polybutadiene rubber having a trans-isomer content of between about 10% and about 60% and present in an amount of from about 5 parts to about 26.5 parts per hundred parts of cis-1,4-polybutadiene rubber; and a cover having a thickness of between about 0.05 inches and about 0.1 inches, the cover consisting essentially of a first ionomeric material and a second ionomeric material; wherein the golf ball has a coefficient of restitution of between about 0.801 and 0.823 when measured at an incoming velocity of 125 ft/s.